Confusion on resource packs and data packs - differences, global or not, etc

I am trying to start the journey of modpack creation. And, so, I am kinda confused - how do I know or understand the difference between a data pack and a resource pack - and among that, which ones to have or need only client side, which one on the server side, and which one have to be available at world creation?

Maybe I am still kinda misunderstanding the purpose of each category, and it surely gets more complicated with the whole introduction of Paxi on one hand, and there is also in Paxi data and resource packs. And on the other hand the fact that regular mod managers like Prism or Curse don't really provide different categories or management of datapacks, and world creation things (or even an overview what is already managed in/by Paxi).

Like, idk, can I just treat everything as both - use every resource and datapack during world creation, and also give each resource and datapack to the client to turn it on there?

I remember playing minecraft and resource packs were only texture and graphic stuff, but now it's more than that, with resource packs also being compat packs and data packs, and I'm just confused if there is a pattern or rule to classification and discernment between all these flavours.